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Effect of hot and cold deformation on the β fiber rolling texture in continuous cast AA 5052 aluminum alloy
Scripta Materialia 52 (2005) 1317–1321 www.actamat-journals.com
Effect of hot and cold deformation on the b fiber rolling texture in continuous cast AA 5052 aluminum alloy W.C. Liu *, J.G. Morris Department of Chemical and Materials Engineering, Light Metals Research Laboratories, University of Kentucky, 177 Anderson Hall, Lexington, KY 40506, USA Received 3 December 2004; received in revised form 2 February 2005; accepted 18 February 2005 Available online 23 March 2005
Abstract The texture evolution of continuous cast AA 5052 aluminum alloy during hot rolling was investigated by X-ray diffraction. The b fiber rolling texture formed under various hot and cold deformation conditions was compared. The results show that deformation at elevated temperatures results in a stronger b fiber rolling texture than that at room temperature. Ó 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Aluminum; Hot deformation; Cold deformation; Texture; X-ray diffraction
1. Introduction The texture evolution of aluminum alloys during rolling has been extensively studied since crystallographic texture is one of the main factors responsible for the mechanical anisotropy of aluminum alloy sheets. In general, during rolling all orientations are rotated to the b fiber, which runs from the B orientation {1 1 0}h1 1 2i through the S {1 2 3}h6 3 4i orientation to the C orientation {1 1 2}h1 1 1i [1]. As the cold rolling reduction increases, the volume fractions of the cube, rotated cube (r-cube), rotated Goss (r-Goss) and remainder components decrease, whereas the volume fraction of the b fiber component increases. The volume fraction of the Goss component first increases with increasing reduction, and then decreases [2]. Alloy composition, initial texture and microstructure affect the texture evolution during rolling, leading to different degrees of the b fiber rolling texture and different distributions of orientation intensity along the b fiber [2,3]. *
Corresponding author. Tel.: +1 859 25 74433; fax: +1 859 323 1929. E-mail address: [email protected] (W.C. Liu).
The effect of deformation temperature and strain rate on the texture evolution during hot deformation has been studied by plane strain compression [4–7]. Panchanadeeswaran and Field [4] observed that the material deformed at an elevated temperature of 375 °C exhibited a significantly stronger texture than that deformed at room temperature for commercial purity aluminum. Duckham et al. [5] also reported that the deformation textures sharpened noticeably with increasing deformation temperature for Al–1%Mg alloy. Vatne et al. [6] studied the stability of cube oriented grains in a hot deformed AA 3004 alloy. Their work demonstrated that the volume fraction of the cube component decreased with increasing value of the Zener–Hollomon parameter, and samples deformed at lower values of Z exhibited a stronger b fiber rolling texture. Samajdar et al. [7] also reported a similar observation for the cube component. However, they found that a decrease in Z value reduced the relative increase in the C and S components, and the change in the B component was relatively small. In the present work the texture evolution of continuous cast (CC) AA 5052 aluminum alloy during hot rolling was investigated by X-ray diffraction. The initial cast
1359-6462/$ - see front matter Ó 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.scriptamat.2005.02.031
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W.C. Liu, J.G. Morris / Scripta Materialia 52 (2005) 1317–1321
slab and the hot rolled bands after each of three rolling passes were obtained from industrial continuous cast processing. Understanding the texture development in the hot rolling process is especially important since the texture that develops during hot rolling has been shown to influence directly the texture of annealed materials entering the cold-rolling mill. The as-received hot bands were then cold rolled to different reductions, which allow the comparison of the b fiber rolling texture under different hot and cold deformation conditions.
maximum tilt angle of 75° by the Schulz back-reflection method using CuKa radiation. The orientation distribution functions (ODFs) were calculated from the incomplete pole figures using the series expansion method (lmax = 16) [8]. The ODFs were presented as plots of constant u2 sections with isointensity contours in Euler space defined by the Euler angles u1, U, and u2. The volume fractions of the texture components were calculated by an improved integration method [2,9,10].
3. Results 2. Experimental 3.1. Structure and texture of continuous cast slab The material used in the present investigation was CC AA 5052 aluminum alloy. The chemical composition of this alloy is given in Table 1. In continuous cast processing, the molten metal is poured between two rotating steel belts to produce a cast slab, and then the slab is immediately fed into three consecutive hot rolling mills, forming hot band products. In order to investigate the texture evolution during the hot rolling process, the continuous cast slab and the hot rolled bands after each of three rolling passes were obtained from an industrial CC processing operation. The thicknesses of the slab and the three hot bands were 21.6, 9.5, 4.1 and 2.1 mm, respectively. The entry rolling temperature was approximately 465 °C. The as-received hot bands with different thicknesses were subsequently cold rolled to 4.1, 2.1, and 1.0 mm on a laboratory rolling mill with a roll diameter of 103 mm. Oil was used as a lubricant. Texture measurements were performed at the center layer of the hot and cold rolled sheets. The (1 1 1), (2 0 0), and (2 2 0) pole figures were measured up to a
Table 1 Chemical composition of CC AA 5052 aluminum alloy (wt%) Alloy 5052
Si 0.115
Fe 0.372
Cu 0.017
Mn 0.055
Mg 2.363
Cr 0.191
Al Bal.
Fig. 1(a) shows a typical grain structure of the continuous cast slab through the thickness. An equiaxed grain structure was observed in the continuous cast slab. The grain size of the slab increased as the measured position moved from the surface to the center. A network of constituent particles was observed in the grain boundaries. It was found that the continuous cast slab contained two types of particles, i.e. the Fe-rich intermetallic particles (Al3Fe and Al6Fe) and the Mg-based intermetallics (Mg2Si) [11]. Fig. 1(b) shows the texture of the continuous cast slab. The texture of the as-cast material was essentially random. No change of texture was observed through the thickness. 3.2. Texture evolution during hot rolling Fig. 2 shows representative sections through the ODFs of hot bands after each of three rolling passes. It is seen that the texture of the hot bands was characterized by the b fiber rolling texture. The strength of the b fiber rolling texture increased with increasing hot rolling true strain. Fig. 3 depicts the texture volume fractions as a function of hot rolling true strain. The volume fractions of the cube, r-cube, r-Goss and remainder components decreased with increasing hot rolling true strain,
Fig. 1. (a) Microstructure and (b) texture at one fifth thickness of the continuous cast slab of AA 5052 aluminum alloy.
W.C. Liu, J.G. Morris / Scripta Materialia 52 (2005) 1317–1321
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Fig. 2. Texture of AA 5052 aluminum alloy under different hot and cold deformation conditions. eh represents the hot rolling true strain, ec the cold rolling true strain, and et the total rolling true strain.
whereas the volume fraction of the b fiber component increased. The volume fraction of the Goss component first increased with increasing hot rolling true strain, and then decreased slightly after the third pass. Compared with the texture evolution of AA 5xxx series aluminum alloys during cold rolling [2], it is noted that the texture evolution during hot rolling was similar to that during cold rolling. 3.3. Effect of hot and cold deformation on the b fiber rolling texture In order to determine the effect of hot and cold deformation on the b fiber rolling texture, the as-received hot
bands with different thicknesses were cold rolled to different strains. The texture of AA 5052 aluminum alloy under various hot and cold deformation conditions is summarized in Fig. 2, and orientation intensities along the b fiber versus the corresponding Euler angle u2 are shown in Fig. 4. After a hot rolling true strain of 0.82, there was a reasonably uniform distribution of orientation intensities along the b fiber. As hot rolling continued further, the level of orientation intensities of the b fiber increased. However, it is noted that the increases in the orientation intensities between the B and S orientations were larger than that at the C orientation. This indicates that initial orientations are easily rotated to the b fiber between the B and S orientations after hot
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80 cube r-cube Goss
60
60 r-Goss β fiber remainder
40
Mβ,%
Texture volume fraction, %
80
40 Hot rolling Cold rolling
20
20
0
0 0
1
2
ε
0
3
1
2 ε
3
4
Fig. 3. Texture volume fractions as a function of hot rolling true strain during the CC processing of AA 5052 aluminum alloy.
Fig. 5. The volume fraction of the b fiber (Mb) as a function of true strain during hot and cold rolling.
rolling to high strains. After the hot band of the first pass was cold rolled to high strains, the maximum intensity of the b fiber was located at u2 = 70°. The orientation intensity of the B orientation was similar to that of the C orientation. Hot and cold deformation affects not only the distribution of orientation intensities along the b fiber, but also the evolution of the b fiber rolling texture. It is seen from Fig. 2 that at a given total strain of 1.66, 2.33, or 3.07, the samples with a hot strain of 1.66 exhibited a stronger b fiber rolling texture than the samples with a hot strain of 0.82, indicating that AA 5052 aluminum alloy has a higher rate of formation of the b fiber during hot rolling than during cold rolling. This situation is further demonstrated in Fig. 5, where the volume fraction of the b fiber is shown as a function of true strain during hot and cold rolling. The effect of hot deformation on the texture evolution depends on the deformation temperature. A decrease in deformation temperature reduces the difference in deformation textures formed during hot and cold rolling. At a given total strain of 2.33 or 3.07, the samples with a hot strain of 2.33 exhibited a similar b fiber rolling texture to the samples with a
hot strain of 1.66. This may be due to low deformation temperature at the third pass.
12 S
10
C
10
C
8
6 εt (εh + εc )
4
50
60
70 ϕ 2, o
80
6
B
εt (εh + εc )
4
0.82 (0.82 + 0) 1.66 (0.82 + 0.84) 2.33 (0.82 + 1.51) 3.07 (0.82 + 2.25)
2
0 40
(b)
B
C
50
60
70 ϕ 2, o
80
6 εt (εh + εc )
4
1.66 (1.66 + 0) 2.33 (1.66 + 0.67) 3.07 (1.66 + 1.41)
2
90
S
8 f (g)
f (g)
f (g)
12
S
B
8
(a)
The cast slab produced in the CC processing possesses an equiaxed grain structure and a random texture. No recrystallization occurs during subsequent hot rolling [2]. Thus, the initial random texture is converted into the b fiber rolling texture due to the effect of deformation. As hot rolling true strain increases, the volume fractions of the cube, r-cube, r-Goss and remainder components decrease, whereas the volume fraction of the b fiber component increases. The variation in texture volume fractions during hot rolling is similar to that during cold rolling. However, it is noted that deformation temperature affects the formation of the b fiber rolling texture. The formation rate of the b fiber during hot rolling is higher than that during cold rolling, leading to a stronger b fiber rolling texture. The observation of a stronger b fiber rolling texture formed during hot deformation is not unique, but is consistent with the
12
10
0 40
4. Discussion
2.33 (2.33 + 0) 3.07 (2.33 + 0.74)
2 0 40
90
(c)
50
60
70
80
90
ϕ 2, o
Fig. 4. Intensities of the ODF f(g) at the center position of the b fiber as a function of a particular angle u2 in AA 5052 aluminum alloy hot rolled and then cold rolled to different strains.
W.C. Liu, J.G. Morris / Scripta Materialia 52 (2005) 1317–1321
experimental observations by Panchanadeeswaran and Field [4], Duckham et al. [5], and Vatne et al. [6], although Samajdar et al. [7] reported that the volume fractions of the C and S components decreased with increase in temperature or decrease in strain rate. This stronger b fiber rolling texture is attributed to a healing out of the dislocations within the subgrains, as well as a consumption of subgrains with scattered orientations during the dynamic recovery that is generally enhanced at higher deformation temperatures [5]. Hot and cold deformation affects the lattice rotation of crystallites and thus the distribution of orientation intensities along the b fiber. Initial orientations are more easily rotated to the S orientation than to the B and C orientations during cold rolling of AA 5052 aluminum alloy. During hot rolling, however, initial orientations are uniformly rotated to the b fiber at a low strains. As hot rolling continues, a few more orientations are rotated to the B orientation, leading to the strongest B component. This is in accordance with experimental observations from the literature [12–14]. The increase in the B component has been attributed to the increase of the strain-rate sensitivity index [12], to the additional activation of other, non-octahedral slip systems at very high deformation temperatures [13], and differential dynamic grain growth [14]. The formation rate of the b fiber depends on the disappearance rates of all initial orientations including the cube, r-cube, Goss, r-Goss, etc. Several researchers have studied the stability of the cube orientation during hot deformation of aluminum alloys [6,7,15]. The stability of the cube orientation increases with decreasing Z value [6,7,15]. Maurice and Driver [16] interpreted the enhanced stability of the cube orientation during hot deformation to be due to the activation of non-octahedral slip systems. Raabe [17] simulated the hot rolling textures of aluminum by means of a Taylor type model which took into consideration dislocation slip on {1 1 1}h1 1 0i and {1 1 0}h1 1 0i slip systems. The results indicated that the cube component was developed at the expense of the B orientation when the yield surface for {1 1 0} slip was within that for {1 1 1} slip, whereas the orientation intensities of the C and S components were not substantially influenced by slip on {1 1 0} h1 1 0i slip systems. However, the effect of hot deformation on the stability of the other orientations is not yet clear. If hot deformation enhanced the stability of all the orientations, the strength of the b fiber rolling texture should decrease with decreasing Z value, which is obviously contrary to the experimental results on the effect of hot deformation on the b fiber rolling texture. Further studies are needed to determine the stability of the r-cube, Goss and r-Goss orientation during hot
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deformation for a better understanding of the texture evolution during rolling. 5. Conclusions The continuous cast slab of AA 5052 aluminum alloy possesses an equiaxed grain structure and a random texture. During hot rolling the initial random texture is converted into the b fiber rolling texture. Deformation temperature affects the formation of the b fiber rolling texture. Deformation at elevated temperatures results in a stronger b fiber rolling texture than that at room temperature. At elevated temperatures initial orientations are more easily rotated to the b fiber between the B and S orientations than to the C orientation, while initial orientations are more easily rotated to the S orientation than to the B and C orientations at room temperature. Acknowledgements The authors would like to acknowledge the financial support of the Air Force Office of Scientific Research (AFOSR) under contract number FA 9550-04-1-0457. Commonwealth Aluminum Corporation, the industrial partner of the project, provided the materials used in the present study. References [1] Hirsch J, Lu¨cke K. Acta Metall Mater 1988;36:2863–82. [2] Liu WC, Morris JG. Metall Trans A 2004;35A:265–77. [3] Liu WC, Zhai T, Man C-S, Radhakrishnan B, Morris JG. Philos Mag 2004;84:3305–21. [4] Panchanadeeswaran S, Field DP. Acta Metall Mater 1995;43:1683–92. [5] Duckham A, Knutsen RD, Engler O. Acta Mater 2001;49:2739–49. [6] Vatne HE, Shahani R, Nes E. Acta Mater 1996;44:4447–62. [7] Samajdar I, Ratchev P, Verlinden B, Aernoudt E. Acta Mater 2001;49:1759–69. [8] Bunge HJ. Texture analysis in materials science. London: Butterworths; 1982. [9] Liu WC, Morris JG. Scripta Mater 2002;47:743–8. [10] Liu WC, Morris JG. Mater Sci Eng A 2003;339:183–93. [11] Wen XY, Zhai T, Long ZD, Xiao CH, Morris JG. In: Jin Z, Beaudoin A, Bieler TR, Radhakrishnan B, editors. Hot deformation of aluminum alloys III. San Diego, California: TMS; 2003. p. 421–31. [12] Engler O, Wagner P, Savoie J, Ponge D, Gottstein G. Scripta Metall Mater 1993;28:1317–22. [13] Maurice C, Driver JH. Acta Mater 1997;45:4627–38. [14] Bate PS, Huang Y, Humphreys FJ. Acta Mater 2004;52:4281–9. [15] Crumbach M, Gottstein G. Mater Sci Eng A 2004;387–389:282–7. [16] Maurice C, Driver JH. Acta Metall Mater 1993;41:1653–64. [17] Raabe D. Acta Metall Mater 1995;43:1023–8.
Effect of hot and cold deformation on the b fiber rolling texture in continuous cast AA 5052 aluminum alloy W.C. Liu *, J.G. Morris Department of Chemical and Materials Engineering, Light Metals Research Laboratories, University of Kentucky, 177 Anderson Hall, Lexington, KY 40506, USA Received 3 December 2004; received in revised form 2 February 2005; accepted 18 February 2005 Available online 23 March 2005
Abstract The texture evolution of continuous cast AA 5052 aluminum alloy during hot rolling was investigated by X-ray diffraction. The b fiber rolling texture formed under various hot and cold deformation conditions was compared. The results show that deformation at elevated temperatures results in a stronger b fiber rolling texture than that at room temperature. Ó 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Aluminum; Hot deformation; Cold deformation; Texture; X-ray diffraction
1. Introduction The texture evolution of aluminum alloys during rolling has been extensively studied since crystallographic texture is one of the main factors responsible for the mechanical anisotropy of aluminum alloy sheets. In general, during rolling all orientations are rotated to the b fiber, which runs from the B orientation {1 1 0}h1 1 2i through the S {1 2 3}h6 3 4i orientation to the C orientation {1 1 2}h1 1 1i [1]. As the cold rolling reduction increases, the volume fractions of the cube, rotated cube (r-cube), rotated Goss (r-Goss) and remainder components decrease, whereas the volume fraction of the b fiber component increases. The volume fraction of the Goss component first increases with increasing reduction, and then decreases [2]. Alloy composition, initial texture and microstructure affect the texture evolution during rolling, leading to different degrees of the b fiber rolling texture and different distributions of orientation intensity along the b fiber [2,3]. *
Corresponding author. Tel.: +1 859 25 74433; fax: +1 859 323 1929. E-mail address: [email protected] (W.C. Liu).
The effect of deformation temperature and strain rate on the texture evolution during hot deformation has been studied by plane strain compression [4–7]. Panchanadeeswaran and Field [4] observed that the material deformed at an elevated temperature of 375 °C exhibited a significantly stronger texture than that deformed at room temperature for commercial purity aluminum. Duckham et al. [5] also reported that the deformation textures sharpened noticeably with increasing deformation temperature for Al–1%Mg alloy. Vatne et al. [6] studied the stability of cube oriented grains in a hot deformed AA 3004 alloy. Their work demonstrated that the volume fraction of the cube component decreased with increasing value of the Zener–Hollomon parameter, and samples deformed at lower values of Z exhibited a stronger b fiber rolling texture. Samajdar et al. [7] also reported a similar observation for the cube component. However, they found that a decrease in Z value reduced the relative increase in the C and S components, and the change in the B component was relatively small. In the present work the texture evolution of continuous cast (CC) AA 5052 aluminum alloy during hot rolling was investigated by X-ray diffraction. The initial cast
1359-6462/$ - see front matter Ó 2005 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.scriptamat.2005.02.031
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W.C. Liu, J.G. Morris / Scripta Materialia 52 (2005) 1317–1321
slab and the hot rolled bands after each of three rolling passes were obtained from industrial continuous cast processing. Understanding the texture development in the hot rolling process is especially important since the texture that develops during hot rolling has been shown to influence directly the texture of annealed materials entering the cold-rolling mill. The as-received hot bands were then cold rolled to different reductions, which allow the comparison of the b fiber rolling texture under different hot and cold deformation conditions.
maximum tilt angle of 75° by the Schulz back-reflection method using CuKa radiation. The orientation distribution functions (ODFs) were calculated from the incomplete pole figures using the series expansion method (lmax = 16) [8]. The ODFs were presented as plots of constant u2 sections with isointensity contours in Euler space defined by the Euler angles u1, U, and u2. The volume fractions of the texture components were calculated by an improved integration method [2,9,10].
3. Results 2. Experimental 3.1. Structure and texture of continuous cast slab The material used in the present investigation was CC AA 5052 aluminum alloy. The chemical composition of this alloy is given in Table 1. In continuous cast processing, the molten metal is poured between two rotating steel belts to produce a cast slab, and then the slab is immediately fed into three consecutive hot rolling mills, forming hot band products. In order to investigate the texture evolution during the hot rolling process, the continuous cast slab and the hot rolled bands after each of three rolling passes were obtained from an industrial CC processing operation. The thicknesses of the slab and the three hot bands were 21.6, 9.5, 4.1 and 2.1 mm, respectively. The entry rolling temperature was approximately 465 °C. The as-received hot bands with different thicknesses were subsequently cold rolled to 4.1, 2.1, and 1.0 mm on a laboratory rolling mill with a roll diameter of 103 mm. Oil was used as a lubricant. Texture measurements were performed at the center layer of the hot and cold rolled sheets. The (1 1 1), (2 0 0), and (2 2 0) pole figures were measured up to a
Table 1 Chemical composition of CC AA 5052 aluminum alloy (wt%) Alloy 5052
Si 0.115
Fe 0.372
Cu 0.017
Mn 0.055
Mg 2.363
Cr 0.191
Al Bal.
Fig. 1(a) shows a typical grain structure of the continuous cast slab through the thickness. An equiaxed grain structure was observed in the continuous cast slab. The grain size of the slab increased as the measured position moved from the surface to the center. A network of constituent particles was observed in the grain boundaries. It was found that the continuous cast slab contained two types of particles, i.e. the Fe-rich intermetallic particles (Al3Fe and Al6Fe) and the Mg-based intermetallics (Mg2Si) [11]. Fig. 1(b) shows the texture of the continuous cast slab. The texture of the as-cast material was essentially random. No change of texture was observed through the thickness. 3.2. Texture evolution during hot rolling Fig. 2 shows representative sections through the ODFs of hot bands after each of three rolling passes. It is seen that the texture of the hot bands was characterized by the b fiber rolling texture. The strength of the b fiber rolling texture increased with increasing hot rolling true strain. Fig. 3 depicts the texture volume fractions as a function of hot rolling true strain. The volume fractions of the cube, r-cube, r-Goss and remainder components decreased with increasing hot rolling true strain,
Fig. 1. (a) Microstructure and (b) texture at one fifth thickness of the continuous cast slab of AA 5052 aluminum alloy.
W.C. Liu, J.G. Morris / Scripta Materialia 52 (2005) 1317–1321
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Fig. 2. Texture of AA 5052 aluminum alloy under different hot and cold deformation conditions. eh represents the hot rolling true strain, ec the cold rolling true strain, and et the total rolling true strain.
whereas the volume fraction of the b fiber component increased. The volume fraction of the Goss component first increased with increasing hot rolling true strain, and then decreased slightly after the third pass. Compared with the texture evolution of AA 5xxx series aluminum alloys during cold rolling [2], it is noted that the texture evolution during hot rolling was similar to that during cold rolling. 3.3. Effect of hot and cold deformation on the b fiber rolling texture In order to determine the effect of hot and cold deformation on the b fiber rolling texture, the as-received hot
bands with different thicknesses were cold rolled to different strains. The texture of AA 5052 aluminum alloy under various hot and cold deformation conditions is summarized in Fig. 2, and orientation intensities along the b fiber versus the corresponding Euler angle u2 are shown in Fig. 4. After a hot rolling true strain of 0.82, there was a reasonably uniform distribution of orientation intensities along the b fiber. As hot rolling continued further, the level of orientation intensities of the b fiber increased. However, it is noted that the increases in the orientation intensities between the B and S orientations were larger than that at the C orientation. This indicates that initial orientations are easily rotated to the b fiber between the B and S orientations after hot
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W.C. Liu, J.G. Morris / Scripta Materialia 52 (2005) 1317–1321
80 cube r-cube Goss
60
60 r-Goss β fiber remainder
40
Mβ,%
Texture volume fraction, %
80
40 Hot rolling Cold rolling
20
20
0
0 0
1
2
ε
0
3
1
2 ε
3
4
Fig. 3. Texture volume fractions as a function of hot rolling true strain during the CC processing of AA 5052 aluminum alloy.
Fig. 5. The volume fraction of the b fiber (Mb) as a function of true strain during hot and cold rolling.
rolling to high strains. After the hot band of the first pass was cold rolled to high strains, the maximum intensity of the b fiber was located at u2 = 70°. The orientation intensity of the B orientation was similar to that of the C orientation. Hot and cold deformation affects not only the distribution of orientation intensities along the b fiber, but also the evolution of the b fiber rolling texture. It is seen from Fig. 2 that at a given total strain of 1.66, 2.33, or 3.07, the samples with a hot strain of 1.66 exhibited a stronger b fiber rolling texture than the samples with a hot strain of 0.82, indicating that AA 5052 aluminum alloy has a higher rate of formation of the b fiber during hot rolling than during cold rolling. This situation is further demonstrated in Fig. 5, where the volume fraction of the b fiber is shown as a function of true strain during hot and cold rolling. The effect of hot deformation on the texture evolution depends on the deformation temperature. A decrease in deformation temperature reduces the difference in deformation textures formed during hot and cold rolling. At a given total strain of 2.33 or 3.07, the samples with a hot strain of 2.33 exhibited a similar b fiber rolling texture to the samples with a
hot strain of 1.66. This may be due to low deformation temperature at the third pass.
12 S
10
C
10
C
8
6 εt (εh + εc )
4
50
60
70 ϕ 2, o
80
6
B
εt (εh + εc )
4
0.82 (0.82 + 0) 1.66 (0.82 + 0.84) 2.33 (0.82 + 1.51) 3.07 (0.82 + 2.25)
2
0 40
(b)
B
C
50
60
70 ϕ 2, o
80
6 εt (εh + εc )
4
1.66 (1.66 + 0) 2.33 (1.66 + 0.67) 3.07 (1.66 + 1.41)
2
90
S
8 f (g)
f (g)
f (g)
12
S
B
8
(a)
The cast slab produced in the CC processing possesses an equiaxed grain structure and a random texture. No recrystallization occurs during subsequent hot rolling [2]. Thus, the initial random texture is converted into the b fiber rolling texture due to the effect of deformation. As hot rolling true strain increases, the volume fractions of the cube, r-cube, r-Goss and remainder components decrease, whereas the volume fraction of the b fiber component increases. The variation in texture volume fractions during hot rolling is similar to that during cold rolling. However, it is noted that deformation temperature affects the formation of the b fiber rolling texture. The formation rate of the b fiber during hot rolling is higher than that during cold rolling, leading to a stronger b fiber rolling texture. The observation of a stronger b fiber rolling texture formed during hot deformation is not unique, but is consistent with the
12
10
0 40
4. Discussion
2.33 (2.33 + 0) 3.07 (2.33 + 0.74)
2 0 40
90
(c)
50
60
70
80
90
ϕ 2, o
Fig. 4. Intensities of the ODF f(g) at the center position of the b fiber as a function of a particular angle u2 in AA 5052 aluminum alloy hot rolled and then cold rolled to different strains.
W.C. Liu, J.G. Morris / Scripta Materialia 52 (2005) 1317–1321
experimental observations by Panchanadeeswaran and Field [4], Duckham et al. [5], and Vatne et al. [6], although Samajdar et al. [7] reported that the volume fractions of the C and S components decreased with increase in temperature or decrease in strain rate. This stronger b fiber rolling texture is attributed to a healing out of the dislocations within the subgrains, as well as a consumption of subgrains with scattered orientations during the dynamic recovery that is generally enhanced at higher deformation temperatures [5]. Hot and cold deformation affects the lattice rotation of crystallites and thus the distribution of orientation intensities along the b fiber. Initial orientations are more easily rotated to the S orientation than to the B and C orientations during cold rolling of AA 5052 aluminum alloy. During hot rolling, however, initial orientations are uniformly rotated to the b fiber at a low strains. As hot rolling continues, a few more orientations are rotated to the B orientation, leading to the strongest B component. This is in accordance with experimental observations from the literature [12–14]. The increase in the B component has been attributed to the increase of the strain-rate sensitivity index [12], to the additional activation of other, non-octahedral slip systems at very high deformation temperatures [13], and differential dynamic grain growth [14]. The formation rate of the b fiber depends on the disappearance rates of all initial orientations including the cube, r-cube, Goss, r-Goss, etc. Several researchers have studied the stability of the cube orientation during hot deformation of aluminum alloys [6,7,15]. The stability of the cube orientation increases with decreasing Z value [6,7,15]. Maurice and Driver [16] interpreted the enhanced stability of the cube orientation during hot deformation to be due to the activation of non-octahedral slip systems. Raabe [17] simulated the hot rolling textures of aluminum by means of a Taylor type model which took into consideration dislocation slip on {1 1 1}h1 1 0i and {1 1 0}h1 1 0i slip systems. The results indicated that the cube component was developed at the expense of the B orientation when the yield surface for {1 1 0} slip was within that for {1 1 1} slip, whereas the orientation intensities of the C and S components were not substantially influenced by slip on {1 1 0} h1 1 0i slip systems. However, the effect of hot deformation on the stability of the other orientations is not yet clear. If hot deformation enhanced the stability of all the orientations, the strength of the b fiber rolling texture should decrease with decreasing Z value, which is obviously contrary to the experimental results on the effect of hot deformation on the b fiber rolling texture. Further studies are needed to determine the stability of the r-cube, Goss and r-Goss orientation during hot
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deformation for a better understanding of the texture evolution during rolling. 5. Conclusions The continuous cast slab of AA 5052 aluminum alloy possesses an equiaxed grain structure and a random texture. During hot rolling the initial random texture is converted into the b fiber rolling texture. Deformation temperature affects the formation of the b fiber rolling texture. Deformation at elevated temperatures results in a stronger b fiber rolling texture than that at room temperature. At elevated temperatures initial orientations are more easily rotated to the b fiber between the B and S orientations than to the C orientation, while initial orientations are more easily rotated to the S orientation than to the B and C orientations at room temperature. Acknowledgements The authors would like to acknowledge the financial support of the Air Force Office of Scientific Research (AFOSR) under contract number FA 9550-04-1-0457. Commonwealth Aluminum Corporation, the industrial partner of the project, provided the materials used in the present study. References [1] Hirsch J, Lu¨cke K. Acta Metall Mater 1988;36:2863–82. [2] Liu WC, Morris JG. Metall Trans A 2004;35A:265–77. [3] Liu WC, Zhai T, Man C-S, Radhakrishnan B, Morris JG. Philos Mag 2004;84:3305–21. [4] Panchanadeeswaran S, Field DP. Acta Metall Mater 1995;43:1683–92. [5] Duckham A, Knutsen RD, Engler O. Acta Mater 2001;49:2739–49. [6] Vatne HE, Shahani R, Nes E. Acta Mater 1996;44:4447–62. [7] Samajdar I, Ratchev P, Verlinden B, Aernoudt E. Acta Mater 2001;49:1759–69. [8] Bunge HJ. Texture analysis in materials science. London: Butterworths; 1982. [9] Liu WC, Morris JG. Scripta Mater 2002;47:743–8. [10] Liu WC, Morris JG. Mater Sci Eng A 2003;339:183–93. [11] Wen XY, Zhai T, Long ZD, Xiao CH, Morris JG. In: Jin Z, Beaudoin A, Bieler TR, Radhakrishnan B, editors. Hot deformation of aluminum alloys III. San Diego, California: TMS; 2003. p. 421–31. [12] Engler O, Wagner P, Savoie J, Ponge D, Gottstein G. Scripta Metall Mater 1993;28:1317–22. [13] Maurice C, Driver JH. Acta Mater 1997;45:4627–38. [14] Bate PS, Huang Y, Humphreys FJ. Acta Mater 2004;52:4281–9. [15] Crumbach M, Gottstein G. Mater Sci Eng A 2004;387–389:282–7. [16] Maurice C, Driver JH. Acta Metall Mater 1993;41:1653–64. [17] Raabe D. Acta Metall Mater 1995;43:1023–8.